The present invention is directed generally to the field of stabilizing serum or plasma samples. The preferred embodiments include compositions that allow retention of at least 80% of the aminotransferase activities in a serum or plasma sample to be retained 48 hours post collection.
Several heart and liver diseases have been correlated with abnormally high levels of serum aspartate aminotransferase (AST). Examples of such conditions include acute myocardial infarction, pulmonary embolism, acute pancreatitis, viral and toxic hepatitis, and acute cirrhosis. Generally speaking, AST is elevated in diseases affecting tissues rich in AST. Similarly, human alanine aminotransferase (ALT) is an enzyme that is leaked into the serum of a patient suffering from hepatic diseases such as viral hepatitis, hepatocirrhosis, etc., and is important as a clinical marker.
Serodiagnosis of ALT and AST is a good indicator of whether a particular subject is undergoing distress in a diseased state. More particularly, the presence of elevated AST or ALT is a good indicator of liver disease. The assays for determining the activity of these enzymes generally involve extracting blood from the subject and immediately employing one of a number of calorimetric or kinetic ultraviolet techniques. Such techniques are described in for example U.S. Pat. Nos. 5,834,226, 5,952,211, and 4,769,323, which describe various assays for aminotransferase activity. A particularly well characterized assay for AST and ALT is that sold by Sigma Chemical Company as part of the aspartate aminotransferase (AST/GOT) test kits.
Regardless of the assay format employed to determine aminotransferase activity, it has been common practice to use these assays on venous blood drawn from the patient in a clinical setting. The assays are performed on serum separated from the whole blood drawn from the patient. This is due to the fact that the aminotransferase activity from red blood cells is sufficiently high to mask the activity present in the serum from other organs. Thus, it is preferable to remove the red blood cells from whole blood in order to obtain an accurate reading of the levels of aminotransferase activity attributable to origins other than the red blood cells.
In addition, aminotransferase enzyme activity in the serum is relatively unstable as a function of time, and, for this reason, it has been common practice to analyze serum relatively quickly once the serum is separated from whole blood. This practice has meant that serodiagnosis for indications of disorders in which the aminotransferase activities are elevated have been performed in the clinical setting as opposed to a setting distant from the hospital.
A need presently exists for a method and system for serodiagnostic purposes, where the sample is stable and retains aminotransferase activity over an extended period of time post collection without the need for additional conditions, such as freeze drying or refrigeration. Such a method would facilitate collection of a sample of blood at a location remote from the location at which analysis is performed. For example, such a method would allow for a patient to collect a sample of blood at home and mail it to diagnostic laboratory for testing.
The preferred method and system described below stabilize blood plasma by separating plasma from whole blood and contacting the plasma with a stabilizing composition. This stabilizing composition is effective to retain an amino transferase activity in the plasma at an activity of at least about 80 percent of initial activity, 48 hours post-collection at a temperature of about 25xc2x0C. The presently preferred stabilizing composition comprises between about 20 mM to about 1 M EDTA and between about 1 mM and about 1 M citrate, when the composition is in solution.
The foregoing paragraphs have been provided by way of introduction, and they are not intended to limit the scope of the following claims.